1. Field of the Invention
This invention relates to the field of data processing systems. More particularly, this invention relates to anti computer virus systems that generate a user warning upon detection of a computer virus.
2. Description of the Prior Art
It is known to provide anti computer virus programs that apply tests for a large number of known virus types and characteristics. If a computer virus is detected, then a warning is issued to the user and the user is given the option to delete, quarantine or clean the infected file.
A computer file infected with a computer virus may contain valuable data and accordingly the ability to clean that file rather than delete it is often highly advantageous. The cleaning and repair of a computer file typically involves the removal of the computer virus code from that file and the reversal of any changes made by that computer virus to the file. However, there are known computer viruses that produce changes to a computer file that cannot be automatically repaired. An example of such a virus is Wazzu which will infect a Word document and insert the text Wazzu at random points within that document as well as swapping the position of some adjacent words within that document. Whilst it may be possible to remove the Wazzu insertions, detecting whether or not particular words within the document have had their positions altered is not something that can automatically be detected with certainty. There are also examples of computer viruses that infect Excel files and will modify data values within cells of that file in a manner that cannot be automatically detected. Depending upon how many times the computer virus has been activated within that file before it is removed, the degree of alteration that may have occurred can vary significantly.